UNITED NATIONS, May 8 (Xinhua) -- U.N. Secretary-General Ban Ki-moon on Thursday expressed his deep concern at the fate of schoolgirls recently abducted in northeastern Nigeria.

"He shares the anguish of the families of the girls and the people of Nigeria at this traumatic time," said a statement issued to the press here by Ban's spokesperson office.

In the statement, Ban reiterated that the targeting of children and schools is against international law and "cannot be justified under any circumstances."

"The secretary-general is following the situation closely and pledges the continued commitment of the United Nations in supporting Nigeria's efforts to tackle internal challenges," the statement said.

"The secretary-general reminds all concerned that human rights law and international humanitarian law must be fully respected," it added.

According to his spokesperson office, the U.N. chief also spoke Thursday by phone with President Goodluck Jonathan of Nigeria.

"He called to personally express his deep concern at the fate of the recently kidnapped schoolgirls in Borno State and to express his solidarity with the people of Nigeria, and especially the girls' families," the spokesperson office said in a separate statement issued here later.

In the phone call, President Jonathan briefed the U.N. secretary-general on the current state of the search for the abducted girls and accepted Ban's offer to send a high-level representative to Nigeria to discuss "how the United Nations can better support the government's efforts to tackle the internal challenges," said the statement.

About 200 girls from Chibok community in northeastern Nigeria's Borno State were abducted in April. On Monday, militant group Boko Haram claimed responsibility for the act in a video and threatened to sell the girls.

In the video, the leader of the Boko Haram, a sect which seeks to enshrine the Islamic Sharia law in the constitution, referred the abducted schoolgirls as "slaves" and said he would sell them " in the market" and "marry them off."

Nigeria, Africa's most populous country, is currently grappling with security challenges, including the insurgency of Boko Haram. Last Thursday, at least 20 people were killed in a blast in the capital Abuja, where the World Economic Forum on Africa will be hosted this week.